1. Field of the Invention
The present invention relates to a travel path displaying apparatus in which a current location and a path of travel of a running body, such as automobile, (hereinafter referred to as a vehicle) are displayed on a display screen which has a map previously displayed thereon.
2. Description of the Prior Art
In an attempt to provide a driving guidance system to prevent a driver of a vehicle from loosing his way in driving, for example in a strange place, from his desired travel path, there has been developed a travel path displaying apparatus including a distance detector for detecting a distance of travel depending upon a running speed of the vehicle and a direction detector for detecting a running direction and an amount of change of direction, from time to time, wherein a current location of the vehicle on two-dimensional coordinates is successively computed from the respective results of detections effected by the above-mentioned detectors and the location thus computed is memorized and displayed in the form of a constantly changing pattern of continuous point informations on a display screen having a map including roads or the like previously displayed thereon, so that the driver may confirm the current location of his vehicle.
In such travel path displaying apparatus, it has been a practice previously to set target points, such as crossing points where the vehicle is to be turned to the right or the left, on a desired travel course from a starting point to a goal on the map, so that the vehicle may be guided in a smooth manner during traveling to the goal.
In such apparatus, however, there is a case where the travel path of the vehicle displayed on the display screen misses the target previously set on the map, owing to a difference between the shape of the roads displayed on the map and the actual shape of the roads. In order to distinguish this case from an erroneous running state where the vehicle is traveling on a path other than the desired travel path, it is desirable to continue the driving guidance on the assumption that the vehicle has passed the target, when the travel path, which has missed the target, satisfies a predetermined condition.
In order to assume that the vehicle has passed the target, it may be possible to set a circular area having a predetermined radius around the target position which has been previously set and registered on the coordinates and to detect the fact that the vehicle comes into said circular area, thereby deciding that the vehicle has passed the target. In this case, where the decision of passing of the vehicle through the target point is made only on the fact that the travel path comes within the predetermined area, if roads in this area are complicated and form a plurality of close crossings, it may be erroneously decided that the vehicle has passed the target at a place other than the target.